If your an SP player let me know if....

[llamabeast]

I don't think rdonj is correct. I believe you use the #allies command to ally a pair of AIs, so using that you can build up several different AI teams.

[Hrum]

I'd be interested in trying this. I like the idea of team games.

I don't have any strong preferences regarding era.

Were you thinking of doing something thematic with regards to nation selection? Ie. the players picking "good" nations (or "evil") or something? Hot vs Cold?